From: Amir Goldstein <amir73il@gmail.com>
To: Kees Cook <keescook@chromium.org>
Cc: syzbot <syzbot+2c49971e251e36216d1f@syzkaller.appspotmail.com>,
Jan Kara <jack@suse.cz>,
Andrew Morton <akpm@linux-foundation.org>,
cai@lca.pw, Chris von Recklinghausen <crecklin@redhat.com>,
LKML <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>,
syzkaller-bugs <syzkaller-bugs@googlegroups.com>
Subject: Re: WARNING: bad usercopy in fanotify_read
Date: Wed, 13 Mar 2019 08:42:25 +0200 [thread overview]
Message-ID: <CAOQ4uxgQf=-swzH_D6cXofXSwXdnpEUsYZ-5q2a_fOZZJy5oRQ@mail.gmail.com> (raw)
In-Reply-To: <CAGXu5jKjWwYk5N3mOH1A8fXX_0BT3r1At_3MzN9M+Ckg5irKXg@mail.gmail.com>
On Wed, Mar 13, 2019 at 8:26 AM Kees Cook <keescook@chromium.org> wrote:
>
> On Mon, Mar 11, 2019 at 1:42 PM syzbot
> <syzbot+2c49971e251e36216d1f@syzkaller.appspotmail.com> wrote:
> > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17ee410b200000
> > [...]
> > ------------[ cut here ]------------
> > Bad or missing usercopy whitelist? Kernel memory exposure attempt detected
> > from SLAB object 'fanotify_event' (offset 40, size 8)!
> > [...]
> > copy_to_user include/linux/uaccess.h:151 [inline]
> > copy_fid_to_user fs/notify/fanotify/fanotify_user.c:236 [inline]
> > copy_event_to_user fs/notify/fanotify/fanotify_user.c:294 [inline]
>
> Looks like this is the fh/ext_fh union in struct fanotify_fid, field
> "fid" in struct fanotify_event. Given that "fid" is itself in a union
> against a struct path, I think instead of a whitelist using
> KMEM_CACHE_USERCOPY(), this should just use a bounce buffer to avoid
> leaving a whitelist open for path or ext_fh exposure.
>
> Maybe something like this (untested):
I tested. Patch is fine by me with minor nit.
You may add:
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
>
> diff --git a/fs/notify/fanotify/fanotify_user.c
> b/fs/notify/fanotify/fanotify_user.c
> index 56992b32c6bb..b87da9580b3c 100644
> --- a/fs/notify/fanotify/fanotify_user.c
> +++ b/fs/notify/fanotify/fanotify_user.c
> @@ -207,6 +207,7 @@ static int process_access_response(struct
> fsnotify_group *group,
> static int copy_fid_to_user(struct fanotify_event *event, char __user *buf)
> {
> struct fanotify_event_info_fid info = { };
> + unsigned char bounce[FANOTIFY_INLINE_FH_LEN], *fh;
> struct file_handle handle = { };
> size_t fh_len = event->fh_len;
> size_t len = fanotify_event_info_len(event);
> @@ -233,7 +234,18 @@ static int copy_fid_to_user(struct fanotify_event
> *event, char __user *buf)
>
> buf += sizeof(handle);
> len -= sizeof(handle);
> - if (copy_to_user(buf, fanotify_event_fh(event), fh_len))
> +
> + /*
> + * For an inline fh, copy through stack to exclude the copy from
> + * usercopy hardening protections.
> + */
> + fh = fanotify_event_fh(event);
> + if (fh_len <= sizeof(bounce)) {
Prefer <= FANOTIFY_INLINE_FH_LEN
> + memcpy(bounce, fh, fh_len);
> + fh = bounce;
> + }
> +
> + if (copy_to_user(buf, fh, fh_len))
> return -EFAULT;
>
> /* Pad with 0's */
>
>
> --
> Kees Cook
next prev parent reply other threads:[~2019-03-13 6:42 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-11 20:42 WARNING: bad usercopy in fanotify_read syzbot
2019-03-13 6:26 ` Kees Cook
2019-03-13 6:42 ` Amir Goldstein [this message]
2019-03-13 14:35 ` Jan Kara
2019-03-13 15:35 ` Kees Cook
2019-03-13 15:47 ` Jan Kara
2019-03-18 18:27 ` Kees Cook
2019-03-19 8:32 ` Jan Kara
2019-03-16 14:49 ` syzbot
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAOQ4uxgQf=-swzH_D6cXofXSwXdnpEUsYZ-5q2a_fOZZJy5oRQ@mail.gmail.com' \
--to=amir73il@gmail.com \
--cc=akpm@linux-foundation.org \
--cc=cai@lca.pw \
--cc=crecklin@redhat.com \
--cc=jack@suse.cz \
--cc=keescook@chromium.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=syzbot+2c49971e251e36216d1f@syzkaller.appspotmail.com \
--cc=syzkaller-bugs@googlegroups.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).